Hydraulic jack

ABSTRACT

A short stroke hydraulic jack for lifting heavy loads. The jack comprises a piston and an open-ended cylinder of substantially equal length, which length is much greater than the length of the stroke of sad piston but much shorter than the respective diameter of the piston and cylinder. The piston is provided on one side with a load-bearing surface and on the other side with axially spaced concentric work surfaces and a centrally disposed shank. The cylinder has an end wall having a central opening therein for receiving said shank and axially spaced surfaces mating with the work surfaces of said piston whereby vertical surface-to-surface contact between the piston and cylinder is maintained in two radially spaced annular areas throughout the length of the stroke of the piston.

United States Patent [151 3,677,518 Buys [45] July 18, 1972 [54] HYDRAULIC JACK Primary Examiner-Robert C. Riordon [72] Inventor. Pieter Buys, Oldenzaal, Netherlands Assistant Examiner David R- Melton [73] Assignee: Applied Power Industries, Inc., Milwau- Attorney-John J. Byme kee, Wis.

22 Filed: Dec. 8, 1970 [57] ABSTRACT A short stroke hydraulic jack for lifting heavy loads. The jack comprises a piston and an open-ended cylinder of substantially equal length, which length is much greater than the US. Cl- R length of the troke of ad piston but much shorter than the [51] Int. Cl. ..B66f 3/24 respective diameter f the piston and cylinden The piston is [58] Field of Search ..254/29 A, 93 R, 93 H; 92/107, provided on one side with a |ad bearing surface and on the 92/108 other side with axially spaced concentric work surfaces and a centrally disposed shank. The cylinder has an end wall having [56] References cued a central opening therein for receiving said shank and axially UNITED STATES PATENTS spaced surfaces mating with the work surfaces of said piston whereby vertical surface-to-surface contact between the Malnwaring H i ton and cylinder is maintained in two radially spaced annu. 2,356,399 8/1944 stutter H lar areas throughout the length of the stroke of the piston. 2,615,233 10/1952 Ferris ....254/93 R 3,338,552 8/1967 Persicke ...254/29 A 4 Claims, 3 Drawing Figures /0 2s -7 f 7 32 l4 /6 *1? mi WW (42 5'7 i I 419 lb 46 b Patented July 18, 197-2 HYDRAULIC JACK This invention relates to a hydraulic jack and more specifically to a hydraulic jack designed to lift extremely heavy loads a very short distance.

There are various uses for heavy-duty hydraulic jacks having a very short stroke length such as one-fourth inch. One particular use is in shipyards where a plurality of jacks are placed at strategic points under the hull of a ship for raising it a fraction of an inch enabling the removal of supporting devices beneath the hull. One of the main problems encountered in lifting such heavy loads is that the piston tends to cant relative to the cylinder thereby causing the piston to bind against the side walls of the cylinder. This is especially true in situations where loads are applied eccentrically to the piston. In placing a jack against a ship hull, for example, it is not always possible to obtain a direct straight line force alignment. This is also particularly true with those jacks wherein the exterior face of the piston itself is the load-bearing surface, as in a disc-type jack. It is this type of jack with which this invention is concerned.

It is an object of this invention to overcome the aforementioned difficulties encountered in prior art piston-cylinder arrangements used in lifting heavy loads.

It is a further object of this invention to provide a hydraulic jack of relatively small size but having a relatively great lifting force of up to 100 tons.

It is still a further object of this invention to provide a shortstroke hydraulic jack for lifting heavy loads having means to minimize binding between the piston and cylinder walls when under eccentric loads.

The objectives of this invention are accomplished by providing a short-stroke hydraulic jack for lifting heavy loads comprising a piston and an open-ended cylinder each of substantially equal length, which length is much greater than the length of the stroke of the piston. This ratio minimizes binding between the piston and the cylinder walls. The exterior face of the piston is provided with a loading-bearing surface and moves partially exteriorly of the cylinder during operation. The interior face of the piston is provided with axially spaced concentric working surfaces and a centrally disposed shank. The bottom or end wall of the cylinder has a central opening for receiving the shank, and axially spaced surfaces for mating with the work surfaces of the piston. Further, means are provided for introducing fluid under extremely high pressures, in the area of 10,000 psi, in the space between the working surfaces of the piston and the end wall of the cylinder. Though there are a plurality of spaced working surfaces, each are in communication with the same fluid pressure source.

These and other objects of the invention will become more apparent to those skilled in the art by reference to the following detailed description when viewed in light of the accompanying drawings wherein:

FIG. 1 is a top plan view of the hydraulic jack of this invention;

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1; and

FIG. 3 is a cross-sectional view taken along lines 33 of FIG. 3.

Referring now to the drawing wherein like numerals indicate like parts, the hydraulic jack of this invention is generally indicated by the numeral 10. With reference to both FIGS. 1 and 2, a piston 12 of substantially disc-like configuration, is nested in a cylindrical recess 14 in a base member 16 which will hereinafter be referred to as a cylinder.

The piston 12 is mounted for reciprocation within the cylinder 16 and defines an expansible chamber 18 therewith which is in communication with a fluid pressure source through inlet 20 and fitting 22. A load-bearing surface 24 is seated in an annular recess 26 in the exterior face 28 of the piston 12. The load-bearing surface has an anti-slip surface thereon and is preferably of a harder material than that of the piston 12. The load-bearing surface or pad 24 is attached to the exterior face of the piston 12 by threaded bolts 32. However, it is to be understood that any suitable means can be used for attaching the pad. In the alternative, the piston may be provided with an integrally formed bearing surface.

The interior face of the piston is provided with axially spaced work surfaces 34 and 36 and a centrally disposed axially extending shank or rod 38. The cylinder 16 is provided with an end wall 40 having axially spaced concentric surfaces 42 and 44 which mate with the work surfaces 36 and 34. Because of the axial spacing of the work surfaces, an annulus 46 is defined around the outer periphery of the piston 12. Similarly an annulus 48 is defined in the end wall 40 and surrounds and defines the central opening 50 which receives the shank 38 of the piston 12. Seals 60 and 62 prevent leakage of fluids from the chamber 18.

In the preferred embodiment, the height of the piston. including the shank 38, or the length thereof if one prefers. is substantially identical to the length or height of the cylinder 16. Further, the surface contact of the vertical sidewall of the piston 12 with the inner surface of the cylinder 16 is several times greater in length than the stroke of the piston within the cylinder. For example, in the preferred embodiment, the total height of the cylinder and also the piston is approximately 2 inches, and the surface contact between the piston 12 and the wall 14 is approximately I 1% inches, while the stroke is only one-fourth inches. This means that substantial lateral support will be maintained between the piston and the cylinder throughout the full stroke of the piston. This is also true with regard to the contact between the annular surface of the shank 38 and the walls of the opening 50. The inner wall of the annulus 46 is spaced from the annulus 48 whereby hydraulic fluid can reach the area under working surface 34. Stop means in the form of a spacer ring 56 is provided on the working surface 36 of the piston 12 to prevent the piston from fully seating. As shown in FIG. 4, the ring is provided with a plurality of spaced, radially extending slots 57 which permit fluid to flow to the area under surface 34. Since the piston does not fully seat and because of the slots 57, fluid can always be maintained underneath the working surfaces to provide instantaneous reaction against the work surfaces upon increasing the pressure in the chamber.

It is to be noted that a substantially high ratio of continuous annular outwardly facing surface-to-surface contact to stroke length is provided at radially spaced points; namely, between the shank 38 and the walls of the central opening 50 and between the peripheral surface of the piston 12 and the wall of the cylinder 16. In operation, when fluid under pressure is introduced into the chamber 18, it is immediately reflected to the area under surface 34 due to the spacing between annuli 46 and 48. If a heavy load is applied eccentrically to the loadbearing surface 24, the tendency of the piston to cant and bind against the walls of the cylinder 16 will be resisted due to the substantial lateral surface contact provided at the above-mentioned radially spaced, outwardly facing contact areas. It is to be pointed out that the vertical height of each of the radially spaced contact areas is many times greater than the full stroke of the piston.

In a general manner, while there has been disclosed an effective and efficient embodiment of the invention, it should be well understood that the invention is not limited to such an embodiment as there might be changes made in the arrangement, disposition, and form of the parts without departing from the printiple of the present invention as comprehended within the scope of the accompanying claims.

lclaim:

l. A hydraulic jack comprising:

a cylinder defining a chamber,

a piston reciprocable in said chamber and snuggly engaging the walls of said cylinder, said piston having exterior and interior faces, a load-bearing surface on said exterior face and concentric axially spaced annular work surfaces on the interior face of said piston,

an end wall in said cylinder opposite said interior face of said piston including concentric, radially spaced, annular surfaces to substantially mate with the concentric work surfaces of said piston,

a source of pressurized fluid, and

means communicating said chamber with said source of pressure.

2. A hydraulic jack as defined in claim 1 wherein said cylinder end wall has a central opening therein and including a centrally disposed shank on the interior face of said piston extending axially into said central opening and snuggly engaging the side walls thereof.

3. A hydraulic jack as defined in claim 2 and wherein the length of the piston including said shank is substantially the same as the length of said cylinder, and the respective diameters of said piston and cylinder are greater than their respective lengths.

4. A hydraulic jack unit comprising a cylinder having a annular side wall and defining a chamber, a piston received in said chamber for reciprocation therein relative to said cylinder,

an end wall in said cylinder,

a centrally disposed first annulus on said end wall defining a central opening therein, said annulus being spaced radially inwardly from said side walls and extending axially into said chamber,

said piston including an exterior face and an interior face opposing said end wall,

a centrally disposed shank on said interior face extending axially therefrom and into said central opening for snug engagement with the side walls thereof and an axially extending second annulus o the outer periphery of said interior fact extending into said space between said first annulus and said side wall, the stroke of said piston being less than the height of each of said first and second annuli, whereby substantial vertical surface-to-surface annular contact is maintained at radially spaced points throughout the length of the stroke of said piston. 

1. A hydraulic jack comprising: a cylinder defining a chamber, a piston reciprocable in said chamber and snuggly engaging the walls of said cylinder, said piston having exterior and interior faces, a load-bearing surface on said exterior face and concentric axially spaced annular work surfaces on the interior face of said piston, an end wall in said cylinder opposite said interior face of said piston including concentric, radially spaced, annular surfaces to substantially mate with the concentric work surfaces of said piston, a source of pressurized fluid, and means communicating said chamber with said source of pressure.
 2. A hydraulic jack as defined in claim 1 wherein said cylinder end wall has a central opening therein and including a centrally disposed shank on the interior face of said piston extending axially into said central opening and snuggly engaging the side walls thereof.
 3. A hydraulic jack as defined in claim 2 and wherein the length of the piston including said shank is substantially the same as the length of said cylinder, and the respective diameters of said piston and cylinder are greater than their respective lengths.
 4. A hydraulic jack unit comprising a cylinder having a annular side wall and defining a chamber, a piston received in said chamber for reciprocation therein relative to said cylinder, an end wall in said cylinder, a centrally disposed first annulus on said end wall defining a central opening therein, said annulus being spaced radially inwardly from said side walls and extending axially into said chamber, said piston including an exterior face and an interior face opposing said end wall, a centrally disposed shank on said interior face extending axially therefrom and into said central opening for snug engagement with the side walls thereof and an axially extending second annulus o the outer periphery of said interior fact extending into said space between said first annulus and said side wall, the stroke of said piston being less than the height of each of said first and second annuli, whereby substantial vertical surface-to-surface annular contact is maintained at radially spaced points throughout the length of the stroke of said piston. 